In many systems there is a need to interface circuitry of one logic family with that of another. For example, it may be necessary to apply signals generated with emitter coupled logic (ECL) devices to metal oxide field effect transistors (MOS). Not only are the ON and OFF states of the two families represented by different voltages, but MOS thresholds are often described as "mushy". By this is meant that MOS does not exhibit a narrow voltage range around some threshold voltage within which a voltage applied to the gate will cause the transistor to turn completely on or completely off. In contrast, bipolar devices usually switch within a fifty to one hundred millivolt region around their threshold voltage, whereas in an MOS device the corresponding region may be one and a half volts. ECL levels however, are commonly from -1.6 v to -0.8 v. It is evident then, that an interface circuit to couple ECL levels to MOS devices must not only take level shifting into account, but must also actually increase the size of the logic swing available from ECL.
In one aspect of the instant invention these objectives are achieved by applying the ECL input to the source of a level-shifter enhancement device whose gate is connected to its drain, which in turn is connected both to the power supply through a load (such as a depletion device) and to the gate of a gain stage comprised of another enhancement device and a load. The output of the gain stage is a signal of three voltages transition suitable for driving MOS logic devices. In another aspect of the invention the source of the gain stage is driven by an ECL signal that is the complement of the ECL signal applied to the source of the level-shifter. By putting the level-shifter on the same substrate as the other MOS circuitry that is to use the converted signals the effects of threshold level changes as a function of temperature are compensated automatically.